Method and apparatus for handoff in a communication system supporting multiple service instances

ABSTRACT

Method and apparatus for effecting handoff in a system supporting both wireless and packet data service communications. In one embodiment, the serving network provides information to the target network sufficient to establish the Point-to-Point Protocol (PPP) connections for handoff. In an alternate embodiment, the serving network and the target network do not share capabilities with respect to concurrent multiple service instances. When the serving network knows the status of the target network, the serving network takes responsibility for the handoff.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is Continuation and claims priorityto patent application Ser. No. 10/095,498 entitled “Method and Apparatusfor Handoff in a Communication System Supporting Multiple ServiceInstances” filed Mar. 11, 2002, now allowed, and assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND FIELD

The present invention relates to wireless communication systemsgenerally and specifically, to methods and apparatus for handoff for apacket data service

BACKGROUND

There is an increasing demand for packetized data services over wirelesscommunication systems. As traditional wireless communication systems aredesigned for voice communications, the extension to support dataservices introduces many challenges. Specifically, the problems existduring handoff involving a Point-to-Point Protocol (PPP) communicationof data packets. As systems upgrade components, compatibility issuesbetween components may hinder operation of the system. Further, there isa desire to remove handoff responsibility from the mobile station andprovide smart handoff by the infrastructure elements.

There is a need, therefore, for fast, accurate handoff between PacketData Service Nodes (PDSNs) and other infrastructure elements in awireless communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a timing diagram illustrating a call flow in a communicationsystem, wherein the Source-PDSN (S-PDSN) and the Target-PDSN (T-PDSN)have similar capability.

FIGS. 2 to 4 are timing diagrams illustrating a call flows incommunication systems, wherein the S-PDSN and the T-PDSN have similarcapability, but are not able to fully negotiate handoff.

FIG. 5 is a timing diagram illustrating a call flow in a communicationsystem, wherein the S-PDSN and the T-PDSN have similar capability,wherein one of the service instances is dormant.

FIG. 6 is a timing diagram illustrating a call flow in a communicationsystem, wherein the Source-PDSN (S-PDSN) and the Target-PDSN (T-PDSN)have similar capability, wherein the Radio Network (RN) triggers variousPoint-to-Point (PPP) connections to effect handoff.

FIG. 7 is a timing diagram illustrating call flow in a communicationsystem, wherein the Target-Radio Network (T-RN) does not supportmultiple service instances.

FIGS. 8 and 9 are timing diagrams illustrating call flow in acommunication system, wherein the T-PDSN does not support multipleservice instances.

FIG. 10 is a block diagram of the communication system supporting IPdata transmissions.

FIG. 11 illustrates communication links involved in a handoff examplefor a system wherein the S-PDSN and the T-PDSN have similar capability.

FIG. 12 illustrates communication links involved in a handoff examplefor a system wherein the S-PDSN and the T-PDSN have differentcapabilities.

FIG. 13 illustrates communication links involved in a handoff examplefor a system wherein the Source-Radio Network (S-RN) and theTarget-Radio Network (T-RN) have different capabilities.

DETAILED DESCRIPTION

The word “exemplary” is used exclusively herein to mean “serving as anexample, instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The following discussion develops the exemplary embodiments by firstpresenting a network implementing mobile IP to communicate data to andfrom a mobile node. Then a spread-spectrum wireless communication systemis discussed. Next, the mobile IP network is shown implemented in thewireless communication system. The messages are illustrated thatregister a mobile node with a home agent thereby enabling IP data to besent to and from the mobile node. Finally, methods for reclaimingresources at the home agent are explained.

Note that the exemplary embodiment is provided as an exemplar throughoutthis discussion; however, alternate embodiments may incorporate variousaspects without departing from the scope of the present invention.Specifically, the various embodiments are applicable to a dataprocessing system, a wireless communication system, a mobile IP networkand any other system desiring efficient use and management of resources.

The exemplary embodiment employs a spread-spectrum wirelesscommunication system. Wireless communication systems are widely deployedto provide various types of communication such as voice, data, and soon. These systems may be based on Code Division-Multiple Access (CDMA),Time Division Multiple Access (TDMA), or some other modulationtechniques. A CDMA system provides certain advantages over other typesof systems, including increased system capacity.

A system may be designed to support one or more standards such as the“TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard forDual-Mode Wideband Spread Spectrum Cellular System” referred to hereinas the IS-95 standard, the standard offered by a consortium named “3rdGeneration Partnership Project” referred to herein as 3GPP, and embodiedin a set of documents including Document Nos. 3G TS 25.211, 3G TS25.212, 3G TS 25.213, and 3G TS 25.214, 3G TS 25.302, referred to hereinas the W-CDMA standard, the standard offered by a consortium named “3rdGeneration Partnership Project 2” referred to herein as 3GPP2, andTR-45.5 referred to herein as the cdma2000 standard, formerly calledIS-2000 MC. The standards cited hereinabove are hereby expresslyincorporated herein by reference.

Each standard specifically defines the processing of data fortransmission from base station to mobile, and vice versa. As anexemplary embodiment the following discussion considers aspread-spectrum communication system consistent with the CDMA2000standard of protocols. Alternate embodiments may incorporate anotherstandard.

A communication system 100 according to one embodiment is shown in FIG.10. The communication system 100 includes both wireless portions andInternet Protocol (IP) portions. The terminology used to describe thevarious elements of the system 100 is intended to facilitateunderstanding of the handoff processes described herein. A MobileStation 120 operating within communication system 100 is first incommunication with a Source-Radio Network (S-RN) 108, wherein the termsource refers to the RN as being the original serving network. The MS120 has established a Service Instance (SI) with S-RN. A serviceinstance refers to a link associated with a service option. For example,a service option may be a packet data link, a Voice over IP (VoIP) link,etc. The S-RN has established an A-10 connection with the Source-PDSN(S-PDSN) 104 via an IP Network 106. The A-10 connection is associatedwith the SI. Note that the various elements of the system, such as theS-PDSN 104, the S-RN 108, and the MS 120, may support only one SI, ormay support multiple SI. Also, within a given system, such as system100, various elements may support only a single SI while other elementssupport multiple SI. The later system configurations may lead toincompatibilities in the capabilities of the various elements, and thuseffect handoff. The S-PDSN 104 is also in communication with an IPNetwork 130. Operation of system 100 may be as specified in the cdma2000Wireless IP Network Standard.

The MS 120 is mobile and may move into an area supported by a Target-RN(T-RN) 118. As the MS 120 is able to communicate with T-RN 118, handoffmay proceed from S-RN 108 to T-RN 118. Once handoff of the wirelessportion of the communication system 100 is completed, the packet dataportion of the system 100 must set up the various PPP links, such as anA-10 connection from T-PDSN 114 to T-RN 118 through IP Network 116. Asdiscussed hereinabove, various scenarios are possible for theconfiguration and handoff processing of a system, such as system 100.

In a first scenario, illustrated in FIG. 1 and with reference to FIG.11, the S-PDSN 104 and the T-PDSN 114 have a same capability withrespect to handling Service Instances (SI). As illustrated in FIG. 11,multiple SI links may be established to both S-PDSN 104 and T-PDSN 114.For multiple SI links, one link is designated as a main link, or PPPlink. The main link is used for setting up the PPP link and is also usedfor signaling associated with the multiple links. The main link is thelink on which the primary packet service instance is connected. It isthe service instance that is first negotiated when establishing thepacket service. This means that the initial PPP negotiation takes placeover this service instance. The primary packet service instance has adirect relation to the packet data session itself. This means thatwhenever there is a packet data session, there's a primary packetservice instance connected to it. The main link is identified as “MAINSI.” Additional links are referred to as auxiliary or secondary links,identified as “AUX SI.” Each link is further defined by an A-10connection to a PDSN.

In the call flow scenario of FIG. 1, the infrastructure elements, S-PDSN104 and T-PDSN 114 successfully handoff the communication with MS 120.The handoff is effected without passing responsibility on to MS 120. Inother words, MS 120 is not required to initiate a new communication atthe target network, such as may have been required if handoff were notsuccessful and the target network would tear down the main SI andauxiliary SI. As in FIG. 1, S-PDSN 104 provides T-PDSN 114 with thenecessary information to establish communication with MS 120. Note thateven though handoff is completed within the radio network or wirelessportion of the system, the packet data portion or IP portion requiresadditional information to set up the various connections required. Forexample, the T-PDSN 114 needs to know which SI is the main SI, as theT-PDSN 114 needs to negotiate PPP set up on the main SI.

FIG. 1 illustrates a call flow associated with fast handoff of oneembodiment. FIG. 1 illustrates a successful case when the handoffhappens between the same revisions of two PDSNs, e.g. both PDSN areimplementing IS-835-B procedures. In this case, there are PDSN to PDSN(P-P) connections established successfully between the Target-PDSN(T-PDSN) and the Serving-PDSN (S-PDSN). In the situation that P-Pconnections can not be established correctly, the normal hard handoffshould occur without tearing the traffic channel. However, if multipleservice instances exist (for example, voice over IP), the target PDSNdoes not know the PPP service instance (main service instance),therefore, it can not initiate PPP negotiation on the correct R-Pconnection. Each labeled step of call flow of FIG. 1 is detailed asfollows:

-   -   A. The mobile station has one or more sessions established to        the Source-Packet Data Service Node (S-PDSN) via the        Source-Radio Network (S-RN). The mobile station may have        multiple service instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. At this time, the mobile        still has airlink traffic channels to the S-RN and an Internet        Protocol (EP) session established to the S-PDSN.    -   C. S-RN sends handoff request message to Target-Radio Network        (T-RN) via Mobile Switching Center (MSC) (not shown).    -   D. The T-RN sends an A11 Registration Request (RRQ) to the        Target-Packet Data Service Node (T-PDSN) including the s bit set        to 1 and the serving P-P address attribute set to the Pi EP        address of the S-PDSN. P-P refers to the connection between the        S-PDSN and the T-PDSN. Pi refers to the PDSN to IP connection.        The s bit indicates simultaneous binding.    -   E. The T-PDSN sends a P-P RRQ including the s bit set to 1 to        the S-PDSN's Pi IP address. The setting of the s bit indicates a        request for a simultaneous binding at the S-PDSN.    -   F. The S-PDSN replies with a P-P Registration Reply (RRP) with        the reply code set to 0. The reply code indicates whether the        operation is successful (or failure). The reply code 0        corresponds to a successful operation, wherein the reply code        other than 0 gives a different failure reason.    -   G. The T-PDSN sends an All RRP with the reply code set to 0 to        the T-RN.    -   H. At this point, forward direction bearer traffic arriving at        the S-PDSN is bicast to the S-RN and the T-PDSN. The T-RN may        buffer the last N packets, where N is implementation dependent.        Reverse direction bearer traffic traverses only the S-RN and the        S-PDSN.    -   I. The S-RN hands off the mobile's Service Instance(s) (Sis) to        the T-RN by sending a handoff direction command to the mobile        station.    -   J. The mobile station handoffs to the T-RN and sends a handoff        completion indication to the T-RN.    -   K. Upon completion of the handoff of the Service Instances        (SIs), the T-RN sends an A11 RRQ with the s bit set to 0 and        including an active start airlink record to the T-PDSN.    -   L. The T-PDSN sends a P-P RRQ with the s bit set to 0 and        including an active start airlink record to the S-PDSN. The        active start airlink record sent is the same one that was        received from the T-RN.    -   M. The S-PDSN replies with a P-P RRP with the reply code set to        0.    -   N. The T-PDSN send an A11 RRP with the reply code set to 0 to        the T-RN.    -   O. At this point, forward direction bearer traffic is tunneled        from the S-PDSN to the T-PDSN over the P-P interface, then        switched onto the appropriate A10 session and delivered to the        T-RN. Reverse direction bearer traffic is sent from the mobile        to the T-RN, then over the appropriate A10 session to the        T-PDSN. The T-PDSN tunnels this traffic over the P-P interface        to the S-PDSN. Note that the P-P session may be periodically        refreshed by the T-PDSN sending a P-P RRQ to the S-PDSN.    -   P. The S-PDSN initiates a teardown of the mobile's A10/A11        session(s) to the S-RN by sending an A11 RUP to the S-RN.    -   Q. The S-RN responds with an A11 RAK.    -   R. The S-RN indicates that the session will be terminated by        sending an A11 RRQ to the S-PDSN with the lifetime set to 0,        including an active stop accounting record. Note that the        accounting record will send to Authentication Authorization and        Accounting (AAA) unit from Serving PDSN. AAA is not shown.    -   S. The S-PDSN indicates that the session is released by sending        an A11 RRP to the S-RN with the lifetime set to 0. Note that the        S-PDSN does not delete the associated PPP context because it is        being used by the mobile via the P-P interface.

In a second scenario, illustrated in FIG. 2, again S-PDSN and T-PDSNshare same capabilities, however, they fail to negotiate the handoff ofthe multiple SI links. The S-PDSN is able to send a message indicatingwhich of the links is the main link. The T-PDSN then takesresponsibility for the handoff and sets up connections for the MS.

Note that the serving PDSN desires to send PPP service instanceindication to the target PDSN in P-P RRP during the period of thesignaling exchange to setup P-P connections. This information may besent regardless of whether P-P connections are setup successfully orunsuccessfully. In the case that the P-P connections establishment failsor later some disconnection between T-PDSN and S-PDSN is detected, thetarget PDSN uses this information to trigger the PPP negotiation on thecorrect R-P connection. FIG. 2 illustrates this type of call flow. Eachlabeled step of call flow of FIG. 1 is detailed as follows:

-   -   A. The mobile station has one or more sessions established to        the S-PDSN via the S-RN. The mobile may have multiple service        instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. Note that the mobile still        has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not        shown).    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. The T-PDSN sends a P-P RRQ including the s bit set to 1 to        the S-PDSN's Pi IP address. The setting of the s bit indicates a        request for a simultaneous binding at the S-PDSN.    -   F. The S-PDSN replies with a P-P RRP with a reply code other        than 0, indicating that the P-P session cannot be established        and indicating the PPP service instance.    -   G. The T-PDSN send an All RRP with the reply code set to 0 to        the T-RN.    -   H. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   I. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   J. Upon completion of the handoff of the service instances, the        T-RN sends an A11 RRQ with the s bit set to 0 and including an        active start airlink record to the T-PDSN.    -   K. The T-PDSN sends an A11 RRP with the reply code set to 0 to        the T-RN.    -   L. The T-PDSN initiates PPP negotiation with the mobile by        sending it an LCP-configure-request.    -   M. PPP negotiation is complete. For simple IP sessions, bearer        traffic may now flow in both directions over the T-RN and        T-PDSN. For MIP sessions, the behavior is as follows below.    -   N. The T-PDSN sends a Mobile IP (MIP) agent advertisement to the        mobile. Note that the mobile may first send a MIP agent        solicitation to the T-PDSN (not shown).    -   O. The mobile sends a MIP RRQ to the T-PDSN.    -   P. The T-PDSN processes the MIP RRQ and then forwards it on to        the HA.    -   Q. If the MIP RRQ is accepted, the HA responds with a MIP RRP        with a reply code of 0.    -   R. The T-PDSN forwards the MIP RRP to the mobile. The mobile may        now send and receive bearer data via its MIP session.

If the target PDSN can not receive the P-P RRP correctly after severalretransmissions, the target PDSN should indicate to the target RN in A11RRP that the operation is failed. In response, the T-RN will release thetraffic channel. In this third scenario, the target PDSN cannot receiveany messages from the serving PDSN, and therefore, the MS releases thetraffic channel. The responsibility for handoff falls to the MS, as theMS initiates the communications, i.e., sessions, with the targetnetwork. Note that for a given system, the radio network level handoffmay have been completed successfully, however, the packet data networklevel must also accomplish a handoff from the S-PDSN to the T-PDSN. Thethird scenario is illustrated in FIG. 3, wherein each labeled step isdescribed as follows:

-   -   A. The mobile station has one or more sessions established to        the S-PDSN via the S-RN. The mobile may have multiple service        instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. Please note that the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not        shown).    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. The T-PDSN sends a P-P RRQ including the s bit set to 1 to        the S-PDSN's Pi IP address. The setting of the s bit indicates a        request for a simultaneous binding at the S-PDSN.    -   F. The T-PDSN does not receive a P-P RRP after a configurable        number of retransmissions of the P-P RRQ.    -   G. The T-PDSN sends an A11 RRP with the reply code set to other        than 0 to the T-RN.    -   H. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   I. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   J. Upon completion of the handoff of the service instances, the        T-RN releases the traffic channel.    -   K. The MS re-initiates the SO33 to setup the traffic channel.        The SO33 refers to the data service option 33 as specified in        IS707.    -   L. T-RN sends A11 RRQ to set up R-P connection.    -   M. T-PDSN replies with All RRP with result code set to ‘0’.    -   N. The MS initiates PPP negotiation with the T-PDSN by sending        it an LCP-configure-request.    -   O. PPP negotiation is complete. For simple IP sessions, bearer        traffic may now flow in both directions over the T-RN and        T-PDSN. For MIP sessions, the behavior is as follows below.    -   P. The T-PDSN sends a MIP agent advertisement to the mobile.        Note that the mobile may first send a MIP agent solicitation to        the T-PDSN (not shown).    -   Q. The mobile sends a MIP RRQ to the T-PDSN.    -   R. The T-PDSN processes the MIP RRQ and then forwards it on to        the HA.    -   S. If the MIP RRQ is accepted, the HA responds with a MIP RRP        with a reply code of 0.    -   T. The T-PDSN forwards the MIP RRP to the mobile. The mobile may        now send and receive bearer data via its MIP session.

In a fourth scenario, the target network, and T-PDSN specifically, isunable to receive handoff information from the source network, andS-PDSN specifically. The target network attempts to set up the PPPconnections via all of the SI links. In other words, since the T-PDSNdoes not know which SI link to use for setting up the PPP connection, itsends the request information on all links. In this case, the T-PDSNsends a Link Control Protocol (LCP) registration message on all SIlinks. In the present example, the MS desires two links, one for packetdata, such as web accesses, and one for Voice over IP (VoIP). The targetPDSN can still indicate the target RN in All RRP that the operation issuccessful. And then the T-PDSN sends LCP Configure Request on all R-Pconnections to trigger the PPP negotiation. The PPP negotiation willoccur over the PPP service instance.

For the secondary packet service instance(s), LCP Configure Request istreated as packet data payload (for example, for Voice over IP, it istreated as RTP payload), therefore, it will be either discarded if theformat is not correct or be passed to the application and is treated aserror. After PPP session is setup, MCFTP can be used for setup thesecondary packet service instance(s). Each labeled step in the call flowof FIG. 4 is described as follows:

-   -   A. The mobile station has one or more sessions established to        the S-PDSN via the S-RN. The mobile may have multiple service        instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. Please note that the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not shown        here).    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. The T-PDSN sends a P-P RRQ including the s bit set to 1 to        the S-PDSN's Pi EP address. The setting of the s bit indicates a        request for a simultaneous binding at the S-PDSN.    -   F. The T-PDSN does not receive a P-P RRP after a configurable        number of retransmissions of the P-P RRQ.    -   G. The T-PDSN sends an All RRP with the reply code set to 0 to        the T-RN.    -   H. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   I. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   J. Upon completion of the handoff of the service instances, the        T-RN sends A11 RRQ to T-PDSN.    -   K. T-PDSN replies with A11 RRP.    -   L. T-PDSN sends LCP Configure Request on all service instances.    -   M. The PPP negotiation only occurs over PPP service instance.    -   N. MCFTP sent over PPP service instance is used for setup flow        treatment and channel treatment for secondary service        instance(s).    -   O. For simple IP sessions, bearer traffic may now flow in both        directions over the T-RN and T-PDSN. For MIP sessions, the        behavior is as follows below.    -   P. The T-PDSN sends a MIP agent advertisement to the mobile.        Note that the mobile may first send a MIP agent solicitation to        the T-PDSN (not shown).    -   Q. The mobile sends a MIP RRQ to the T-PDSN.    -   R. The T-PDSN processes the MIP RRQ and then forwards it on to        the HA.    -   S. If the MIP RRQ is accepted, the HA responds with a MIP RRP        with a reply code of 0.    -   T. The T-PDSN forwards the MIP RRP to the mobile. The mobile may        now send and receive bearer data via its MIP session.

In a fifth scenario, illustrated in FIG. 5, the MS again desiresmultiple Sis, specifically two, however, the main PPP SI is dormant.While the main SI is dormant, the corresponding A10 is still in place.For the Dormant Service Instance, the MS is responsible to triggerDormant Handoff after detecting the Packet Zone ID (PZID) is changedupon receiving In-traffic System Parameter Message (ISPM) from thetraffic channel. The PZID identifies the packet data network supportingthe MS. There are two problems with this scenario. First, if the MSfails to receive the ISPM, the call is dropped as there is no A10 and noP-P connection for the PPP Service Instance. Second, the dormant serviceinstance has to be transitioned to the Active state. The dormant servicemay not be required, and therefore making it active to accomplishhandoff is a waste of resources. Each labeled step is illustrated inFIG. 5, and described as follows:

-   -   A. The mobile station has multiple sessions established to the        S-PDSN via the S-RN. The mobile station has multiple service        instance(s) in Dormant (for example, PPP service Instance) and        has multiple service instances active and allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. At this time, the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not shown        here).    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. The T-PDSN sends a P-P RRQ including the s bit set to 1 to        the S-PDSN's Pi IP address. The setting of the s bit indicates a        request for a simultaneous binding at the S-PDSN.    -   F. The S-PDSN replies with a P-P RRP with the reply code set to        0.    -   G. The T-PDSN sends an A11 RRP with the reply code set to 0 to        the T-RN.    -   H. At this point, forward direction bearer traffic arriving at        the S-PDSN is bicast to the S-RN and the T-PDSN for the Active        Service Instance. The T-RN may buffer the last N packets, where        N is implementation dependent. Reverse direction bearer traffic        traverses only the S-RN and the S-PDSN.    -   I. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   J. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   K. Upon completion of the handoff of the service instances, the        T-RN sends an A11 RRQ with the s bit set to 0 and including an        active start airlink record to the T-PDSN.    -   L. The T-PDSN sends a P-P RRQ with the s bit set to 0 and        including an active start airlink record to the S-PDSN. The        active start airlink record sent is the same one that was        received from the T-RN.    -   M. The S-PDSN replies with a P-P RRP with the reply code set to        0.    -   N. The T-PDSN sends an All RRP with the reply code set to 0 to        the T-RN.    -   O. The T-RN sends system information via In-Traffic System        Parameter Message (ISPM) including the new Packet Zone ID        (PZID).    -   P. The MS detects PZID is changed, the MS will send an Ehanced        Origination Message (EOM) to set up SO33 which is main service        instance as an example.    -   Q. The T-RN sends A11 RRQ to setup A10 connection.    -   R. The T-PDSN sends P-P RRQ to setup P-P connection.    -   S. The S-PDSN replies with P-P RRP.    -   T. The T-PDSN replies with A11 RRP.    -   U. T-RN sends service connect to the MS to connect PPP service        instance.    -   V. The MS replies with service connect completion.    -   W. Upon the PPP service instance is connected, T-RN sends A11        RRQ to start accounting record.    -   X. The T-PDSN sends P-P RRQ to S-PDSN.    -   Y. The S-PDSN replies with P-P RRP.    -   Z. T-PDSN replies with A11 RRP.    -   AA. At this point, forward direction bearer traffic for both PPP        service instances and Secondary Service Instance are tunneled        from the S-PDSN to the T-PDSN over the P-P interface, then        switched onto the appropriate A10 session and delivered to the        T-RN. Reverse direction bearer traffic is sent from the mobile        to the T-RN, then over the appropriate A10 session to the        T-PDSN. The T-PDSN tunnels this traffic over the P-P interface        to the S-PDSN. Note that the P-P session may be periodically        refreshed by the T-PDSN sending a P-P RRQ to the S-PDSN.    -   BB. The S-PDSN initiates a teardown of the mobile's A10/A11        session(s) to the S-RN by sending an A11 RUP to the S-RN.    -   CC. The S-RN responds with an A11 RAK.    -   DD. The S-RN indicates that the session will be terminated by        sending an A11 RRQ to the S-PDSN with the lifetime set to 0,        including an active stop accounting record.    -   EE. The S-PDSN indicates that the session is released by sending        an A11 RRP to the S-RN with the lifetime set to 0. Note that the        S-PDSN does not delete the associated PPP context because it is        being used by the mobile via the P-P interface.

In a sixth scenario, illustrated in FIG. 6, when the P-P Connection issuccessfully established for secondary Service Instances with S-PDSN,S-PDSN is responsible to trigger the set up of P-P connection fordormant PPP service instance or other dormant service instances as theS-PDSN has knowledge as to which service is in Dormant Mode. The T-PDSNmay start to trigger the set up of A10 connections for the dormantservice instances. The labeled steps of the call flow of FIG. 6 aredescribed as follows:

-   -   A. The mobile station has multiple sessions established to the        S-PDSN via the S-RN. The mobile station has multiple service        instance(s) in Dormant (for example, PPP service Instance) and        has multiple service instances active and allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. At this time, the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not shown        here).    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. The T-PDSN sends a P-P RRQ including the s bit set to 1 to        the S-PDSN's Pi IP address. The setting of the s bit indicates a        request for a simultaneous binding at the S-PDSN.    -   F. The S-PDSN replies with a P-P RRP with the reply code set to        0.    -   G. The T-PDSN sends an A11 RRP with the reply code set to 0 to        the T-RN.    -   H. Because S-PDSN knows PPP service instance is in Dormant mode,        S-PDSN will sends P-P RRQ to T-PDSN to set up P-P connection.    -   I. T-PDSN replies with P-P RRP with result code set to ‘0’.

There are two options here.

-   -   Option 1:    -   J. The T-PDSN sends A11 RUP to T-RN to request for establishing        R-P connection for PPP service Instance.    -   K. The T-RN replies with A11 RAK.    -   L. Then the T-RN sends A11 RRQ to set up A10 connection.    -   M. T-PDSN replies with A11 RRP with code set to ‘0’.    -   Option 2:    -   N. The T-PDSN sends A11 RRQ to establish R-P connection for PPP        service Instance.    -   O. The T-RN replies with A11 RRP with code set to ‘0’.    -   P. At this point, forward direction bearer traffic arriving at        the S-PDSN is bicast to the S-RN and the T-PDSN for both PPP        Service Instance and Secondary Service Instance. The T-RN may        buffer the last N packets, where N is implementation dependent.        Reverse direction bearer traffic traverses only the S-RN and the        S-PDSN.    -   Q. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   R. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   S. Upon completion of the handoff of the service instances, the        T-RN sends an A11 RRQ with the s bit set to 0 and including an        active start airlink record to the T-PDSN.    -   T. The T-PDSN sends a P-P RRQ with the s bit set to 0 and        including an active start airlink record to the S-PDSN. The        active start airlink record sent is the same one that was        received from the T-RN.    -   U. The S-PDSN replies with a P-P RRP with the reply code set to        0.    -   V. The T-PDSN send an A11 RRP with the reply code set to 0 to        the T-RN.    -   W. At this point, forward direction bearer traffic for both PPP        service instances and Secondary Service Instance are tunneled        from the S-PDSN to the T-PDSN over the P-P interface, then        switched onto the appropriate A10 session and delivered to the        T-RN. Reverse direction bearer traffic is sent from the mobile        to the T-RN, then over the appropriate A10 session to the        T-PDSN. The T-PDSN tunnels this traffic over the P-P interface        to the S-PDSN. Note that the P-P session may be periodically        refreshed by the T-PDSN sending a P-P RRQ to the S-PDSN.    -   X. The S-PDSN initiates a teardown of the mobile's A10/A11        session(s) to the S-RN by sending an A11 RUP to the S-RN.    -   Y. The S-RN responds with an A11 RAK.    -   Z. The S-RN indicates that the session will be terminated by        sending an A11 RRQ to the S-PDSN with the lifetime set to 0,        including an active stop accounting record.    -   AA. The S-PDSN indicates that the session is released by sending        an A11 RRP to the S-RN with the lifetime set to 0. Note that the        S-PDSN does not delete the associated PPP context because it is        being used by the mobile via the P-P interface.

The scenarios and examples discussed hereinabove assume a same versionof protocols for the serving network and the target network. In otherwords, these examples and scenarios assumed that the S-PDSN and theT-PDSN had similar capabilities. For example, each was able to supportmultiple Service Instances.

Consider the situation where the packet data networks and/or the radionetworks do not have similar capabilities, but rather, one is able tohandle multiple SIs, while the other is not.

When the serving network has capability to support multiple SIs, and thetarget network does not, the system must determine which one toterminate and how to effect such termination. For example, when thehandoff occurs from low revision PDSN (IS-835 Release A or lower) tohigh revision PDSN (IS-835 Release B or higher), there are no problemsbecause IS-835-A PDSN can only support one packet data service instance.In this case, after handoff to the target PDSN, the secondary serviceinstances can be setup. When the serving network has capability for onlya single SI, as specified in IS-95. Also cdma2000 Release 0 specifiessupport for a single SI. Starting from cdma2000 Release A, multiple SIare specified to be supported, and the target has capability formultiple SIs, the responsibility is on the MS to initiate the additionalSIs with the target network after handoff.

A seventh scenario is illustrated in FIG. 7 and with respect to FIG. 13,wherein the target radio network, T-RN, is not able to support multipleSIs. Note that the serving radio network, S-RN, knows that the targetnetwork cannot support sessions that are active in the serving networkprior to handoff. For example, when the handoff occurs from highrevision PDSN (IS-835 Release B or higher) to low revision PDSN (IS-835Release A or lower), if there are secondary service instancesestablished, how to handle these multiple service instances becomes aproblem. In this situation, because the serving RN knows the target RNcannot support concurrent services (multiple R-P connections), theserving RN only performs handoff for the main service instance (PPPService instance) to T-RN. The MS may also indicate to the user that thesecondary service instances are dropped because of roaming to a lowerrevisions area. Each of the labeled steps in the call flow of FIG. 7 isdescribed as follows:

-   -   A. The mobile station has one or more sessions established to        the S-PDSN via the S-RN. The mobile may have multiple service        instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. Please note that the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not        shown).    -   D. Because S-RN knows the T-RN cannot support concurrent        service, S-RN hands off the mobile's PPP service instance to the        T-RN by sending handoff direction command to the mobile station.    -   E. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   F. Upon completion of the handoff of the service instances, the        T-RN sends an A11 RRQ with the s bit set to 0 and including an        active start airlink record to the T-PDSN.    -   G. The T-PDSN sends an A11 RRP with the reply code set to 0 to        the T-RN.    -   H. The T-PDSN initiates PPP negotiation with the mobile by        sending it an LCP-configure-request.    -   I. PPP negotiation is complete. For simple IP sessions, bearer        traffic may now flow in both directions over the T-RN and        T-PDSN. For MIP sessions, the behavior is as follows below.    -   J. The T-PDSN sends a MIP agent advertisement to the mobile.        Note that the mobile may first send a MIP agent solicitation to        the T-PDSN (not shown).    -   K. The mobile sends a MIP RRQ to the T-PDSN.    -   L. The T-PDSN processes the MIP RRQ and then forwards it on to        the HA.    -   M. If the MIP RRQ is accepted, the HA responds with a MIP RRP        with a reply code of 0.    -   N. The T-PDSN forwards the MIP RRP to the mobile. The mobile may        now send and receive bearer data via its MIP session.

FIG. 13 illustrates the system 100 including a T-PDSN 144, which may becapable of multiple SIs, but is illustrated supporting the one SIallowed by T-RN 148. After successful handoff to the target network, themain SI is established with T-RN 148 and the associated A10 connectionis established between T-RN 148 and T-PDSN 144.

In an eight scenario, illustrated in FIG. 8 and with respect to FIG. 12,the target RN can support concurrent service, i.e., multiple serviceinstances, but the corresponding T-PDSN can not support multiple serviceinstances. As illustrated in the call flow of FIG. 8, the T-RN sends anA11 RRQ to request for bicasting upon handoff is requested by the S-RN.Since the old revision of T-PDSN doesn't support P-P connection andbicasting establishment, the T-PDSN will send A11 RRP to indicatefailure. In this case, T-RN doesn't know which is PPP service instance,the T-RN has to release traffic channel. The MS should indicate the usercall is dropped because of roaming to the low revision area. If needed,the MS will start to set up SO33 from the beginning. Each of the labeledstep of FIG. 8 is described as follows:

-   -   A. The mobile station has one or more sessions established to        the S-PDSN via the S-RN. The mobile may have multiple service        instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. Please note that the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not shown        here).    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. Since the T-PDSN does not support fast P-P interface handoff,        the T-PDSN sends an A11 RRP with the reply code set to other        than 0 to the T-RN.    -   F. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   G. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   H. Upon completion of the handoff of the service instances, the        T-RN releases the traffic channel since it doesn't know which        service instance is PPP service instance.    -   I. The MS re-initiates the SO33 to setup the traffic channel.    -   J. T-RN sends A11 RRQ to set up R-P connection.    -   K. T-PDSN replies with A11 RRP with result code set to ‘0’.    -   L. The MS initiates PPP negotiation with the T-PDSN by sending        it an LCP-configure-request.    -   M. PPP negotiation is complete. For simple EP sessions, bearer        traffic may now flow in both directions over the T-RN and        T-PDSN. For MIP sessions, the behavior is as follows below.    -   N. The T-PDSN sends a MIP agent advertisement to the mobile.        Note that the mobile may first send a MIP agent solicitation to        the T-PDSN (not shown).    -   O. The mobile sends a MIP RRQ to the T-PDSN.    -   P. The T-PDSN processes the MIP RRQ and then forwards it on to        the HA.    -   Q. If the MIP RRQ is accepted, the HA responds with a MIP RRP        with a reply code of 0.    -   R. The T-PDSN forwards the MIP RRP to the mobile. The mobile may        now send and receive bearer data via its MIP session.

FIG. 12 illustrates the system 100 including a T-PDSN 134 which is notcapable to support multiple sessions. Therefore, even though, the T-RN118 may support multiple SIs, only the main SI has a corresponding A10connection established with T-PDSN 134.

In a ninth scenario, illustrated in FIG. 9, during the handoff betweenT-RN and S-RN, the PPP service instance information is also exchanged.Therefore, when The T-RN receives failure indication from T-PDSN, theT-RN only release the secondary service instance and keep the PPPservice instance connected. Each of the labeled steps of the call flowof FIG. 9 is described as follows:

-   -   A. The mobile station has one or more sessions established to        the S-PDSN via the S-RN. The mobile may have multiple service        instances allocated in the S-RN.    -   B. The mobile station detects the pilot signal strength changes        and sends pilot reports to the S-RN. Please note that the mobile        still has airlink traffic channels to the S-RN and an IP session        established to the S-PDSN.    -   C. S-RN sends handoff request message to T-RN via MSC (not shown        here). Also the S-RN indicate the PPP service instance to T-RN.    -   D. The T-RN sends an A11 RRQ to the T-PDSN including the s bit        set to 1 and the serving P-P address attribute set to the Pi IP        address of the S-PDSN.    -   E. Since the T-PDSN does not support fast P-P interface handoff,        the T-PDSN sends an A11 RRP with the reply code set to other        than 0 to the T-RN.    -   F. The S-RN hands off the mobile's service instance(s) to the        T-RN by sending handoff direction command to the mobile station.    -   G. The mobile station handoffs to the T-RN and sends handoff        completion indication to the T-RN.    -   H. Since the T-RN knows which service instance is PPP service        instance, the T-RN sends A11 RRQ to set up R-P connection for        PPP service instance.    -   I. T-PDSN replies with A11 RRP with result code set to ‘0’.    -   J. The T-RN also sends service connect to the MS to release the        Secondary Service Instance and maintain the PPP Service        Instance.    -   K. T-PDSN will trigger the PPP negotiation by sending LCP        Configure Request.    -   L. PPP negotiation is complete. For simple IP sessions, bearer        traffic may now flow in both directions over the T-RN and        T-PDSN. For MIP sessions, the behavior is as follows below.    -   M. The T-PDSN sends a MIP agent advertisement to the mobile.        Note that the mobile may first send a MN agent solicitation to        the T-PDSN (not shown).    -   N. The mobile sends a MIP RRQ to the T-PDSN.    -   O. The T-PDSN processes the MIP RRQ and then forwards it on to        the HA.    -   P. If the MW RRQ is accepted, the HA responds with a MIP RRP        with a reply code of 0.    -   Q. The T-PDSN forwards the MWP RRP to the mobile. The mobile may        now send and receive bearer data via its MN session.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method in a communication system, comprising: establishing a firstlink between a wireless device and a first server via a first radionetwork; establishing a second link between the wireless device and thefirst server via the first radio network, the first link and the secondlink corresponding to separate connections between the first server andthe first radio network; and initiating a handoff from the first radionetwork to a second radio network.
 2. The method of claim 1, furthercomprising: establishing a first link and a second link between thewireless device and the second server.
 3. The method of claim 2, furthercomprising: sending a Point-to-Point Protocol (PPP) configurationrequest from the second server to the wireless device.
 4. The method ofclaim 1, wherein the first link is associated with a first serviceinstance, and the second link is associated with a second serviceinstance.
 5. The method of claim 4, wherein the second service instanceis a Voice over Internet Protocol service.
 6. The method of claim 1,further comprising: sending a message to a second server identifying thefirst link.
 7. The method of claim 6, wherein the first server and thesecond server incorporate the same protocols.
 8. The method of claim 1,wherein the step of initiating the handoff from the first radio networkto the second radio network further comprising: sending a pilot reportfrom the wireless device to the first radio network.
 9. The method ofclaim 8, further comprising: sending a handoff message form the serviceradio network to the second radio network.
 10. The method of claim 9,wherein the pilot report identifies a pilot signal strength.
 11. Themethod of claim 1, wherein the message is a reply to a registrationrequest.
 12. A method in a communication system comprising: establishinga first link between a wireless device and a first server via a firstradio network; establishing a second link between the wireless deviceand the first server via the first radio network, the first link beingseparate from the second link; initiating a handoff from the first radionetwork to a second radio network; receiving a registration request fromthe second radio network; sending a link initiation message to thewireless device on the first link via the second radio network, thefirst link associated with a first service instance; and sending thelink initiation message to the wireless device on a the second link viathe second radio network, the second link associated with a secondservice instance.
 13. The method of claim 12, wherein the first link isa Point-to-Point Protocol (PPP) connection.
 14. The method of claim 13,wherein the second link is an auxiliary link for Voice over InternetProtocol.
 15. The method of claim 12, further comprising: requestingregistration from a first server.
 16. A method, comprising: establishinga first link between a wireless device and a first server via a firstradio network; establishing a second link between the wireless deviceand the first server via the first radio network, the first link and thesecond link corresponding to separate connections between the firstserver and the first radio network; initiating a handoff from the firstradio network to a second radio network, the first radio network adaptedto support multiple service instances, the second radio network adaptedto support one service instance; terminating the second link to thefirst radio network; sending first link information of the first radionetwork to the second radio network; and performing the handoff to thesecond radio network.
 17. A method, comprising: establishing a firstlink between a wireless device and a first server via a first radionetwork, establishing a second link between the wireless device and thefirst server via the first radio network, the first link and the secondlink corresponding to separate connections between the first server andthe first radio network; initiating a handoff from the first radionetwork to a second radio network, the first radio network coupled to afirst server adapted to support multiple service instances, the secondradio network coupled to a second server adapted to support one serviceinstance; sending first link information of the first radio network tothe second radio network; and performing the handoff to the second radionetwork.
 18. An apparatus in a communication system, comprising: meansfor establishing a first link between a wireless device and a firstserver via a first radio network, and for establishing a second linkbetween the wireless device and the first server via the first radionetwork, the first link and the second link corresponding to separateconnections between the first server and the first radio network; meansfor initiating a handoff from the first radio network to a second radionetwork; and means for sending a message to a second server identifyingthe first link.
 19. An apparatus in a communication system, comprising:means for establishing a first link between a wireless device and afirst server via a first radio network, and for establishing a secondlink between the wireless device and the first server via the firstradio network, the first link and the second link corresponding toseparate connections between the first server and the first radionetwork; means for initiating a handoff from the first radio network toa second radio network; means for receiving a registration request froma the second radio network; means for sending a link initiation messageto a the wireless device on a the first link via the second radionetwork, the first link associated with a first service instance; andmeans for sending the link initiation message to the wireless device ona the second link via the second radio network, the second linkassociated with a second service instance.
 20. An apparatus in acommunication system, comprising: means for establishing a first linkbetween a wireless device and a first server via a first radio network,and establishing a second link between the wireless device and the firstserver via the first radio network, the first link and the second linkcorresponding to separate connections between the first server and thefirst radio network; and means for initiating a handoff from the firstradio network to a second radio network.
 21. A server configured to:establish a first link between a wireless device and a first server viaa first radio network; establish a second link between the wirelessdevice and the first server via the first radio network, the first linkand the second link corresponding to separate connections between thefirst server and the first radio network; and initiate a handoff fromthe first radio network to a second